In any wireless communication network there is a continued effort to achieve higher data exchange rates. Typically, digital data is exchanged wirelessly in the form of packets between two devices communicating with each other. Such packets are also commonly referred to as frames and represent a sequence of bits making up the digital information.
Referring briefly to FIG. 1, a packet 20 typically includes a preamble 22, a data field 24 and an error detecting field 26. The preamble 22 includes a synchronization pattern (not shown) which allows a device receiving the packet 20 effectively to lock-on to the packet 20. The preamble 22 also typically includes a number of other control fields (not shown) which include such information as the source address, destination address, etc., of the packet 20. The data field 24 includes the particular digital information intended to be communicated, sometimes referred to as the "payload". The error detecting field 26 is normally located at the end of the packet as a means for checking the accuracy of a given transmission. For example, a cyclical redundancy code (CRC) value is commonly included in the error detecting field 26.
A maximum length of a packet is determined primarily based on system tolerances for acceptable data bit error rate (BER) or frame error rate (FER) for transmissions between two devices. The longer in length the packet or frame, the more likelihood there will be an error which would require the packet to be re-transmitted.
A receiving device attempting to receive a frame or packet must determine whether the current signal-to-noise ration (S/N ratio) associated with a particular receiving antenna is sufficiently strong to receive the packet being transmitted. In receivers having two or more antennas which allow for antenna diversity, the S/N ratio associated with different antennas may differ thereby allowing the packet to be received by one antenna and not the other. The selection of which of several antennas to use while receiving a packet is conventionally done once at the start of reception of a packet. The selected antenna is then used to receive the remainder of the packet regardless of whether conditions change in the system which would otherwise have made one of the other antennas a better candidate for receiving at least a portion of the remainder of the packet.
In order to avoid having frame errors which would require the re-transmission of an entire packet, data in packets are often divided into several smaller packets having shorter lengths. For example, FIG. 2 illustrates the manner in which the data field 24 of the packet 20 in FIG. 1 can be divided into n (e.g., n=3) smaller packets. Each smaller packet includes a corresponding portion (e.g., 24a-24c) of the original data field 24. The smaller length packets are then transmitted separately together with a corresponding preamble 22 and its own error detecting field 26 as represented in FIG. 2.
By having smaller packet lengths, overhead associated with re-transmitting a single, long length packet may be reduced. Overhead associated with re-transmitting a packet may, for example, include the time it takes the receiving device to transmit a negative-acknowledgment indicating improper reception, time in generating another identical packet for transmission, and any additional time associated with waiting for the air to clear before re-transmitting the packet. By initially dividing data up into several packets having shorter lengths, time associated with transmitting and receiving the negative-acknowledgment can at least be avoided.
Unfortunately, even with dividing data up into several smaller packets, much of the overhead discussed can still exist. For instance, in order to send two consecutive packets which are relatively short in length the transmitting device must wait for an acknowledgment associated with transmission of a first packet before attempting to transmit a second packet. Additionally, even after receiving the acknowledgment, the transmitting device must still wait for the air to clear before transmission can begin for the second packet. Further, for each additional packet that is transmitted, there is extra overhead associated with including the preamble field and the detecting field.
In view of the aforementioned shortcomings associated with conventional data transmission, there is a strong need in the art for an improved method and apparatus which allows for reduced overhead associated with transmitting data. In particular, there is a strong need in the art for an apparatus and method which does not sacrifice data throughput.